Saturday, May 16, 2009

Air Conditioning (cont.)

Karen and I have decided to buy an air conditioner. I don't want to because it's not a fun toy like a new camera gadget, video game system, or LEGO set. Also, it's expensive. However, Hawaii is hot and will be getting hotter for us since we lose exterior windows in July and August (see previous post).

When I have to buy something that I don't want to, I delay the purchase by reading about it. Trying to learn something about before I go in and make the purchase. Air conditioning is no exception.

Air conditioners come in all shapes and sizes. Growing up in metro Atlanta, Georgia, I was used to central air conditioning. Air conditioning was an absolute must in that region of the country and when it broke down, it sucked. Central air conditioners measure their cooling capacity in tons. At one point in time, I assumed all air conditioners were measured this way. It wasn't until college that I learned room air conditioners are measured in BTUs. But wait, isn't that British thermal unit? Yes, it is. And I can make the drive to Home Depot in less than 12 parsecs.

First, you have to be able to understand air conditioning measurements. Tons vs. BTUs is pretty simple. One ton of air conditioning capacity is equal to 12,000 BTUs of air conditioning. And one BTU is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. Wait, what?

The take away from above is that BTUs are the core unit for air conditioning capacity. More BTUs means more capacity for cooling. Simple. Now, how do you determine how many BTUs (or tons) you need? The answer is you make a wild ass guess using random bullshit factors and some arithmetic.

The HVAC industry has divided the country up in to zones. These zones take in to consideration year round climate, high and low temperatures, and humidity levels. The zones are assigned bullshit factors which you use to multiply the number of square feet you want to cool by to arrive at a BTU value. Hawaii isn't given a zone because all of the zone maps I found are for the continental United States. So I picked Florida's zone. That means I use a bullshit multiply factor of 40 (according to the zone map I found).

We primarily want to cool two rooms in the condo, but not at the same time. The largest room is 150 square feet. 150 times 40 is 6,000 BTUs. The average window mounted air conditioner is 10,000 BTU, so figure these things are pretty inefficient and suffer a lot of loss in the cooling process.

But what about heat loss and ventilation where you want to cool and the building insulation and whether or not you have a glass wall that the sun beats down on for most of the day or if you high ceilings or hardwood floors or carpet? Yeah, I dunno. It's a bullshit figure to help you pick out an air conditioner.

Armed with the number 6,000, I plan to head to Home Depot later to get something near that cooling capacity. Pictures of the set up to be posted later.